A monsoon forecast from the Department of Hydro-Met Services, MoEA forecasts that this year the expected start of monsoon is in the second week of June.
The annual total rainfall is forecasted to be normal to below normal. Normal for Bhutan is the mean total rainfall for 18 years from 1996-2013. The monsoon rainfall (June-Sept) is forecasted to be 5.1% below the normal. Monthly rainfall for June and July is forecasted to be below normal and for Aug and Sept is above normal. Overall, the monsoon rains (June-Sept) is predicted to be slightly more than last year.
The monsoon will start from the south and advance towards the central and northern parts of the country. As in the past more rain is expected in Phuntsholing, Samdrupjongkhar, Gelephu and Samtse.
Bhutan and neighboring countries receive rainfall from the large-scale seasonal southwesterly winds blowing from the Bay of Bengal and the Arabian Sea. The SW monsoon accounting to 72% of the total rainfall in Bhutan has a huge importance for the economy and the livelihood of the people. The main aim of the report is to provide forecasts on rainfall that will benefit among others the hydro power sector and the farmers.
The report is on the seasonal forecast for rainfall in Bhutan for 2014 by using the Climate Predictability Tool (CPT) and statistical analysis and verified from the regional outlooks. The outlook is for the whole of Bhutan and the distribution of the past observational data is highlighted. The outlook is mainly for the whole monsoon season (June-Sept) and monthly variations within the monsoon season. The spatial variations within Bhutan among different districts and daily variations including rainfall extreme events are beyond the scope of the report.
Historical data is from the 20 meteorological stations from each district treated as representative for Bhutan and is available from 1996-2013 (18 years). From the observational records the highest amount of the monthly total rainfall occurred in July followed by June and August, and lowest in December. Seasonally the monsoon rain in the months of June-September accounts for 72% of the total annual rainfall. The station-wise distribution shows that the highest amount of annual total rainfall occurred at Sipsu south-western part of Bhutan (5492 mm) and the lowest occurred at Thimphu (602 mm) and Paro (599mm). Sipsu, Phuntsholing, Bhur, and Deothang all in south Bhutan received the highest amounts of rainfall compared with the rest of the country.
There is statistically significant 80% likelihood of a normal to below normal annual total rainfall in 2014. From the CPT outputs the rainfall forecasts for June is about 17% below, for July is about 7 % below, August is about 30% above and September is about 7% above the normal rainfall of respective months. Normal for Bhutan is the mean total rainfall for 18 years from 1996-2013. The normal rain for the month of JJAS from 1996 to 2013 for Bhutan is 1308.3 mm. The forecast of rain anomaly for JJAS 2014 for Bhutan is 1241 mm, and the forecast is about 5.1 % below the normal. JJAS rainfall is normal within the range of ±10%. The onset of monsoon in Bhutan is normally on 5th June with ±5 days. Based on the IMD sources this year the onset is predicted to be likely around the 10th June ±5days.